1. Field of the Invention
The invention relates to a system for counteracting the effect of helicopter vibrations on a seat in the helicopter, which seat includes a plurality of controllable air cells. More specifically, the invention relates to such a system wherein the effects of the vibrations are counteracted by controllably adjusting the pressure in the air cells to counteract the changes in pressure in the air cells due to the vibrations.
2. Description of Prior Art
Sustained helicopter vibration can have harmful and injurious effects to the pilot of the helicopter and can adversely affect the pilot's comfort and performance. As eliminating or even reducing the vibrations is difficult and possibly even impossible, the only feasible approach to eliminating the harmful effects to the pilot is to counteract the effect of helicopter vibrations. The most reasonable approach is to counteract the effect of vibrations on the pilot seat in the helicopter.
For this purpose, an "active" seat is proposed, that is, a seat having a plurality of controllable air cells. Such seats are known in the art as illustrated in, for example, U.S. Pat. No. 3,270,440, Radosevic, Jr., Sept. 6, 1966, U.S. Pat. No. 4,059,909, Kron, Nov. 29, 1977, U.S. Pat. No. 3,983,640, Cardullo et al, Oct. 5, 1976, and U.S. Pat. 4,164,079, Ashworth, Aug. 14, 1979. The above patents all relate to seats for flight simulators, and the pressure of the controllable air cells is typically varied by, for example, hydraulic actuators and bellows. However, the seats are controlled to simulate pressures which would be felt due to the forces of acceleration of an aircraft in a simulated situation, and the pressures are controlled by computers which control the pressure in the air cells and in concert control other parameters of the flight simulators to give the impression of an aircraft in flight.
A similar approach is used in U.S. Pat. No. 3,097,436, Gaucher, July 16, 1963 except that here the pressure of fluid sacs which are attached to fixed walls in the simulator are used to provide the users of the simulator with a simulated feeling of motion.
Various approaches are known in the art for isolating a first body, which is connected to a second body, from the effects of vibration of the second body. One such approach is illustrated in U.S. Pat. No. 3,202,388. However, as can be seen, this is an entirely mechanical approach and would not be suitable for use in a helicopter environment.
A further approach from isolating a first body from a second body is illustrated in U.S. Pat. No. 3,701,499, Schubert et al, Oct. 31, 1972. This patent teaches an aircraft with an active seat, that is a seat which is adapted to be manipulated so as to reduce the effects of vibrations of the aircraft on the pilot sitting in the seat. However, in this case, it is the seat itself which is isolated from the aircraft. In fact, the pilot and the seat are considered as a single integral unit.
Although the approach in U.S. Pat. No. 3,701,499 yields satisfactory results, it is a difficult and expensive approach to implement. In fact, it requires a new seat mounting. As the position and nature of the seat mounting is a structural effect, implementing a seat of the type as taught in the patent requires not only a redesign of the seat but of the entire helicopter structure. As can be appreciated, substantial costs are involved in implementing this approach.
In addition, the seat in this approach remains unchanged so that it is not possible with the teachings of the U.S. Pat. No. 3,701,499, to provide differential pressures to different parts of the body of the pilot in the seat.
As will also be appreciated, it would be impossible to use the approach of U.S. Pat. No. 3,701,499 for the purpose of simply retro-fitting helicopters, or, more specifically, the seats in the helicopters. As mentioned, because of the structural effect of implementing this approach, and not only the seat, but the entire helicopter, must be redesigned.